You mean go over the pink and purple lines without any blocks? Yes, you can do that. If you mean go over other blocks, then... you can, but it would change the texture of the other blocks that you go over, too.
The game will only read colors from specific places. If you draw something outside those specific squares, then your work will either not display ingame at all, or it will display in the wrong places; on the wrong blocks.
Texture pack making